For its part, the Salt Lake Cityâ''based Sarcos team, led by roboticist and inventor Stephen C. Jacobsen, has been working on what may be one of the strongest exoskeletons ever built. Earlier this year, at the demonstration the group did in Fort Belvoir, an engineer wearing the Sarcos robotic system was able to carry 84 kg [185 lb]â''about the weight of an average size washing machineâ''without feeling the payload at all. Jacobsen, Sarcos's CEO and a mechanical engineering professor at the University of Utah, says that the new exoskeleton supports the payload's entire weight even if the wearer stands on one leg.

Like Bleex 2 [the UC Berkeley exo], the latest Sarcos system is a second-generation model that improves substantially over its predecessor. Jacobsen says that while wearing the exoskeleton, you can walk and run, and if you stumble, the system is fast enough to readjust its powered limbs to keep the payload's weight off your body.

The exoskeleton relies on a network of force sensors that are in touch with the wearer's body at certain points, such as underneath the feet. These special sensors, developed by Sarcos, feed data to a control computer that in turn commands the robotic limbs to move in harmony with the wearer's arms and legs without ever obstructing them. Jacobsen calls this method "get out of the way" control, and he says using the robotic suit requires no training. "You can step into the exoskeleton, and you can immediately run it," he says.

According to Jacobsen, what makes an exoskeleton an extremely hard problem is that conventional, off-the-shelf components won't work. Sarcos had to design and fabricate each piece and, in parallel, integrate all of them into its system. The exoskeleton's power unit was one of these many pieces the company had to engineer painstakingly. It's a special internal-combustion engine that can use a variety of fuels and deliver enough hydraulic power to the actuators to meet the great strength and speed the robotic limbs require.

But even more challenging, Jacobsen says, was developing yet another component: the servo valves that control the flow of the hydraulic fluid into the actuators. The valves had to be small, extremely reliable, resistant to high pressures, and highly efficient to preserve precious power, not to mention that some of their parts had to be machined to micrometer tolerances. To make things even harder, so many complex physical processes occur in the valves, Jacobsen insists that simulation software couldn't help in the design. His group, therefore, had to go through several iterations of prototypes to get the valve it needed.

Sarcos is now preparing for demonstrations scheduled over the next few months. Team members are especially busy with the exoskeleton's upper-extremity system, which will add strength to the wearer's arms. A person wearing the full-body system will be able not only to carry a payload on a backpack but also lift heavy items, a capability that is particularly useful for logistics operations such as loading and unloading cargo vehicles and moving things in a warehouse.

PS: When my colleague Harry Goldstein and I spoke with Sarcos for that article, the company had just began developing their exoskeleton's upper-extremity part. Now, as the video shows, it seems they've made significant progress. One thing, however, hasn't changed. Note in the video: the exo has a tether attached to it, probably feeding power or control signals to the suit. Sure, it's a prototype. It will be interesting to see how exoskeleton researchers will cut the umbilical cords of their creations.